1. Field of the Invention
The present invention relates to an illumination structure in a microscope.
2. Prior Art
In a common optical system of a microscope, a light flux reflected from a target area to be viewed is guided through an objective lens and a set of different lenses to an eyepiece for having an enlarged view of the target area.
FIG. 8 shows one of such known optical systems (which is disclosed in German Patent Application laid open under No. 2932486), in which a pair of objective lenses 20 and 21 are provided; the lower 20 is fixed and the upper 21 is vertically movable. Upward and downward movements of the upper objective lens 21 varies the focal length of the optical system. The upper objective lens 21 has a slit 23 provided therein for accepting a light shielding sheet 24. While the light shielding sheet 24 is anchored to a prism P, it allows the upper objective lens 21 to vertically move along.
A flux of viewing light L is returned along the center axis of the two objective lenses 20 and 21. An illumination light R is projected through the prism P along a tilted path separated by the light shielding sheet 24. Since the path of the illumination light R is separated by the light shielding sheet 24, no straying portion of the illumination light R will interfere the viewing light L.
However, the illumination light R in the conventional microscope is projected at an angle to and off the center axis of the objective lenses 20 and 21 thus creating shadows on the target area or if the target area is deep and narrow, hardly reaching the lowermost of the target area.
It is recently required for allowing more than one person to view the target area simultaneously or recording the target area with a video camera or the like while viewing it to guide and distribute the viewing light L as a group of separate beams through their respective lenses. As shown in FIG. 8, the objective lenses 20 and 21 are limited in use since their specific region defined by the light shielding sheet 24 is used for passing the illumination light R, and allow the viewing light L to pass across the remaining region. Hence, a desired number of separate beams of the viewing light L will hardly be obtained.
The present invention has been developed in view of such a prior art and its object is to provide an illumination structure in a microscope capable of illuminating the lowermost of a deep, narrow target area to be viewed and distributing the viewing light as a desired number of separate beams with ease.